Abstract

In recent years, with continuous development of wireless communication technology, LTE,Wi-Fi, satellite communications, cooperative communications and other signs of emergingtechnologies have emerged one after another. Since these communication technologies call for ahigher demand on spectrum resources so that the spectrum resources become strained, cognitiveradio (Cognitive Radio, CR) technology emerges in this context. Based on software-defined radio,the CR is able to use and share of idle spectrum opportunistically, and then solve the problem ofspectrum resource shortage so as to achieve the purpose of improving spectrum utilization really.In order to achieve the recognition of signal modulation type of authorized users and avoiddisrupting the normal communication of the primary user, the CR system requirements itselfshould have cognitive ability and reconfigure function. Therefore, there has an extremely importantsignificance for studying of signal modulation recognition problems in cognitive radio.As a key technology of CR system, spectrum sensing technology is important for detectingpresence of authorized users’ signals. Due to factors of multipath fading, shadow effects and noise,detection rate of individual cognitive user can’t meet the requirements of detecting authorizeduser’s signal in fact. Therefore, in recent years, some scholars, in order to effectively reduceadverse effects of external factors on the authorized user’s signal detection, have proposed newalgorithms when multi-users participate in cooperative spectrum sensing. The article firstlyintroduces the existing spectrum sensing algorithms and studies some unfavorable factors’ impacton the performance of the algorithms to detect. Secondly, the paper studies two improvedcooperative spectrum sensing algorithms, simulates and studies the experiment. Finally, the paperresearches and analysis some factors, such as the number of users in cooperative cognitive, impacton the performance of the algorithm.Since signal modulation recognition can provide reliable reconstruction parameters for re-configuration of CR system, so the article describes, simulates and analysis recognition algorithmsof common signal modulation. In recognition of signal modulation type, characteristic parametersextracted should have good anti-noise performance. Analyzing of signal characteristic parameters,the paper proposes an improved modulation recognition algorithm. From the experimentalsimulation results, not only features extracted shows better anti-noise performance, but alsomodulation recognition algorithm improved shows better recognition performance, and achieves a high recognition rate.